If a traditional mobile phone is powered on and set to a using mode such as dialing a call or inputting a short message, a plurality of light emitting devices such as a light emitting diode (LED) installed in the mobile phone will obtain power. After the light emitting components have obtain power to produce a light, the light is projected to a keyboard and a screen of the mobile phone to illuminate the keyboard and the screen, so that a mobile phone user can clearly see the words, icons, and the like on the keyboard and the screen while the user is dialing a call, receiving a short message, or playing a game.
However, the design of the light emitting components on the mobile phone produces a light source with a constant brightness only, regardless of the environment, so that if the mobile phone is used in an environment with strong sunlight, the light emitting component still produces the light source with a constant brightness. Such arrangement not only wastes power, but also reduces the life of the light emitting components. Furthermore, if the mobile phone is used at nighttime, the light emitting component still produces a light source with the constant brightness, and such bright light will affect other people. Therefore, finding a way of designing a communication device with an adjustable brightness is an important subject that demands immediate attention and feasible solutions.